Isobaric VaporâLiquid Equilibrium for the Binary and Ternary System

Article pubs.acs.org/jced

Isobaric Vapor−Liquid Equilibrium for the Binary and Ternary System with Isobutyl Alcohol, Isobutyl Acetate and Dimethyl Sulfoxide at 101.3 kPa Haofei Liu, Xianbao Cui,* Ying Zhang, Tianyang Feng, and Kai Zhang State Key Laboratory of Chemical Engineering (Tianjin University), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China ABSTRACT: The isobaric vapor−liquid equilibrium (VLE) data for the binary systems isobutyl alcohol + dimethyl sulfoxide (DMSO), isobutyl acetate + DMSO, and ternary system isobutyl alcohol + isobutyl acetate + DMSO were measured at 101.3 kPa. All of the binary VLE data passed Wisniak’s modifed Herington area test and Wisniak point and area test. Ternary VLE data passed Wisniak point test. The VLE data of binary systems were correlated with NRTL, UNIQUAC, and Wilson models. The ternary VLE behavior were successfully predicted by the correlated binary parameters. The VLE data for the binary and ternary systems predicted by the correlated interaction parameters were in good agreement with all the experimental data. The relative volatility of isobutyl acetate to isobutyl alcohol can be greatly increased by DMSO and the azeotropic point of isobutyl acetate and isobutyl alcohol will disappear if the mole fraction of DMSO is greater than 0.36. DMSO is a promising solvent for separating the azeotrope of isobutyl alcohol and isobutyl acetate by extractive distillation.

1. INTRODUCTION Isobutyl acetate is widely used in chemical and pharmaceutical industries,1 such as coatings, inks, adhesives, industrial cleaners, and degreasers. Isobutyl acetate is produced by esterification of acetic acid with isobutyl alcohol. However, isobutyl alcohol and isobutyl acetate can form a minimum boiling point azeotrope (isobutyl alcohol 0.875, mole fraction) at 101.3 kPa,2 which causes difficulty for the subsequent purification of isobutyl acetate. There are many strategies to separate the azeotropes, such as pressure-swing distillation,3,4 azeotropic distillation,5 extractive distillation.6−10 Among them, extractive distillation is the most widely used technology. With the addition of a solvent (entrainer), the relative volatility can be altered, which makes the azeotrope broken. Thus, the selection of a suitable entrainer becomes the key problem before the separation process is designed. So far, many entrainers have been investigated to separate isobutyl alcohol and isobutyl acetate, such as 1hexanol,11 butyl propionate,12,13 and N,N-dimethylformamide.14 Dimethyl sulfoxide (DMSO) is a high polar solvent and can dissolve a lot many organic and inorganic chemicals. DMSO can be used to separate many azeotropes.6−10 It was reported that DMSO was an effective solvent to separate isobutyl alcohol and isobutyl acetate.15,16 Isobaric VLE data of the system of isobutyl alcohol, isobutyl acetate, and DMSO are essential for the simulation and design of an extractive distillation column. So far, the isobaric VLE data of isobutyl alcohol and isobutyl acetate have been reported.2 Betancourt et al.17 measured the © XXXX American Chemical Society

VLE data of isobutyl alcohol and DMSO under the temperatures of 80.0, 92.5, and 105.0 °C. However, the isobaric VLE data for isobutyl alcohol + DMSO, isobutyl acetate + DMSO, and isobutyl alcohol + isobutyl acetate + DMSO cannot be found in open literatures. In this paper, the isobaric VLE data for isobutyl alcohol + DMSO, isobutyl acetate + DMSO, and isobutyl alcohol + isobutyl acetate + DMSO were measured. Thermodynamic consistency tests for all of the binary VLE data were carried out by Wisniak’s modified Herington area method and Wisniak method, and ternary VLE data was carried out by Wisniak point method. The binary VLE data were correlated with NRTL, UNIQUAC, and Wilson models. The correlated binary parameters were used to predict the ternary VLE behavior and compared with the measured data.

2. EXPERIMENTAL SECTION 2.1. Materials. All the chemicals used in this work were purchased from chemical reagent company. Isobutyl alcohol, isobutyl acetate, and DMSO were analyzed by gas chromatography (GC) with a FID detector (Beifen Ruili SP-1000) and the mass fraction were greater than 0.995. The water content determined by Karl Fischer titration was below 500 ppm. The purity of the chemicals was further verified by comparing their normal boiling point (Tb) at 101.3 kPa and measured density Received: March 7, 2017 Accepted: May 11, 2017

A

DOI: 10.1021/acs.jced.7b00241 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

prepared standard solution using an electronic balance (Mettler-Toledo AL204, standard uncertainty of 0.1 mg). The standard uncertainty of gas chromatographic composition analysis was below 0.001 in mole fraction

(ρ) at 298.15 K with corresponding literature values. The normal boiling point was measured by all glass dynamics recirculating still using a calibrated thermometer with an uncertainty of 0.05 K. The density was measured using the Anton Paar DMA-58 density meter with an accuracy 0.0001 g/ cm3. All the corresponding information was listed in Tables 1 and 2. All the chemicals in this work were used directly without further purification.

3. RESULT AND DISCUSSION 3.1. Experimental Data. The VLE measurements were carried out in a dynamic recirculating still. To test the

Table 1. Materials Descriptiona components isobutyl alcohol isobutyl acetate DMSO

CAS

supplier

78-83-1 110-19-0 67-68-5

Guangfu. China Guangfu. China Xiensi. China

purity (mass %)

water (mass %)

analysis method

99.8

0.02

GCb KFc

99.8

0.03

GCb KFc

99.9

0.00

b

GC KF

Table 3. Experimental VLE Data of the System Isobutyl Alcohol (1) + Isobutyl Acetate (2) at Pressure P = 101.3 kPa, Temperature T, Liquid Mole Fraction x, Vapor Mole Fraction ya

c

a

Standard uncertainties: u(purity) = 0.001; u(water) = 0.0001. bGC = gas chromatography. cKF = Karl Fischer titration.

Table 2. Normal Boiling Points (Tb) at 101.3 kPa and Densities (ρ) at 298.15 K for Isobutyl Alcohol, Isobutyl Acetate, DMSOa Tb (K)

a

ρ (298.15 K) (g/cm3)

components

this work

literature

this work

literature

isobutyl alcohol

380.98

0.7980

isobutyl acetate

389.90

DMSO

463.85

381.0912 381.1524 389.9012 389.8524 464.007 463.456

0.798223 0.797925 0.866326 0.866111 1.095327 1.096228

0.8662 1.0955

Standard uncertainties: u(T) = 0.05 K, u(ρ) = 0.0001 g/cm3

T/K

x1

y1

ΔT/Kb

Δy1c

389.90 388.55 387.79 387.17 385.73 384.88 383.56 382.97 382.83 382.37 381.95 381.88 381.34 380.96 380.74 380.82 380.56 380.32 380.51 380.98

0.000 0.049 0.077 0.092 0.180 0.230 0.321 0.362 0.393 0.431 0.499 0.533 0.620 0.648 0.728 0.755 0.835 0.856 0.909 1.000

0.000 0.085 0.127 0.152 0.270 0.334 0.419 0.460 0.483 0.513 0.576 0.607 0.670 0.685 0.749 0.772 0.844 0.858 0.902 1.000

0.24 0.16 0.09 0.20 −0.21 −0.13 −0.17 0.28 0.02 0.27 0.04 0.05 0.22 0.27 −0.26 −0.20 0.26 0.10 0.12 0.14

0.000 0.000 −0.001 0.002 0.003 0.010 0.001 0.003 0.000 −0.003 0.003 0.007 0.002 −0.004 −0.003 −0.001 0.004 0.001 −0.005 0.000

a

Standard uncertainties: u(x) = 0.001, u(y) = 0.001, u(T) = 0.05 K, u(P) = 0.1 kPa. bΔT = Texp − Tcal. cΔy1 = y1exp − y1cal.

2.2. Apparatus and Procedure. The VLE data for both binary and ternary system were measured in an all glass dynamics recirculating still, and the details of the apparatus and measurement procedure were described in our previous publications.18−22 The pressure of the still was maintained at 101.3 kPa by a circulating water vacuum pump (Yu Hua SHZD(III), provided by Yu Hua Instrument, China) and measured by a manometer with standard uncertainty 0.1 kPa. The temperature was determined with a standard and calibrated thermometer with standard uncertainty 0.05 K. The vapor liquid equilibrium was usually reached when the temperature fluctuation was within 0.1 K in about 30 min. Samples of the equilibrium phases were withdrawn from the vapor and liquid sampling points and analyzed, respectively. 2.3. Sample Analysis. The condensed vapor and liquid samples were analyzed by gas chromatograph (Beifen Ruili SP1000) with an FID detector. The GC is equipped with a Wel30 GC capillary column (50 m in length, 0.32 mm in diameter, and 5.0 μm in thickness, chromatographic support: 100% dimethyl polysiloxane, provided by Welch Materials, Inc., Shanghai China.). The operating conditions were as follows: the temperatures of injector, oven, and detector were 503.15, 413.15, and 513.15 K, respectively. The flow rate of carrier gas (nitrogen) was 30 mL/min, and the flow rates of hydrogen and air were 30 mL/min and 300 mL/min, respectively. For liquid and condensed vapor, the real concentrations of isobutyl alcohol, isobutyl acetate, and DMSO were calibrated by calibration factors, which were determined from a set of

Figure 1. Isobaric VLE data of the system isobutyl alcohol (1) + isobutyl acetate (2) at 101.3 kPa: ●, experimental data; ○, literature2 data; dash line, calculated result with NRTL model.

equilibrium apparatus, isobaric VLE data of isobutyl alcohol and isobutyl acetate were measured at 101.3 kPa. VLE data and absolute deviation were shown in Table 3. Figure 1 indicated B



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Table 4. Experimental VLE Data of the System Isobutyl Alcohol (1) + DMSO (3) at Pressure P = 101.3 kPa, Temperature T, Liquid Mole Fraction x, Vapor Mole Fraction y, Activity Coefficient γa T/K

x1

y1

463.85 455.11 452.15 447.81 444.18 439.03 433.32 430.01 425.40 421.00 418.40 414.70 411.65 407.71 404.25 400.81 397.54 394.45 392.92 389.58 386.99 383.06 380.98

0.000 0.038 0.052 0.075 0.097 0.128 0.168 0.193 0.233 0.274 0.304 0.342 0.379 0.430 0.479 0.532 0.587 0.645 0.675 0.748 0.817 0.920 1.000

0.000 0.236 0.306 0.400 0.474 0.565 0.649 0.693 0.749 0.793 0.821 0.851 0.875 0.901 0.922 0.940 0.954 0.966 0.972 0.982 0.989 0.996 1.000

γ1 0.752 0.756 0.759 0.753 0.770 0.778 0.784 0.794 0.807 0.807 0.827 0.839 0.856 0.874 0.893 0.912 0.931 0.941 0.962 0.970 0.998 1.000

Table 5. Experimental VLE Data of the System Isobutyl Acetate (2) + DMSO (3) at Pressure P = 101.3 kPa, Temperature T, Liquid Mole Fraction x, Vapor Mole Fraction y, Activity Coefficient γa

γ3

T/K

x2

y2

1 1.002 1.000 1.000 0.995 0.990 0.993 0.990 0.985 0.985 0.970 0.962 0.952 0.935 0.916 0.892 0.863 0.829 0.810 0.765 0.701 0.635

463.85 452.16 444.19 433.25 428.67 426.65 421.33 415.33 411.04 408.59 407.02 404.36 401.81 400.19 398.48 397.86 396.65 396.20 394.90 394.31 393.65 392.95 392.11 391.32 389.90

0.000 0.019 0.036 0.072 0.093 0.103 0.135 0.188 0.239 0.279 0.319 0.382 0.462 0.532 0.595 0.620 0.671 0.707 0.763 0.794 0.831 0.868 0.894 0.919 1.000

0.000 0.285 0.437 0.612 0.665 0.690 0.738 0.799 0.836 0.853 0.868 0.884 0.903 0.910 0.922 0.928 0.934 0.943 0.950 0.956 0.963 0.970 0.974 0.980 1.000

a

Standard uncertainties: u(x) = 0.001, u(y) = 0.001, u(T) = 0.05K, u(P) = 0.1 kPa.

γ2

γ3 1.000 0.996 0.997 0.985 1.002 0.999 1.035 1.035 1.040 1.067 1.071 1.140 1.203 1.357 1.444 1.452 1.610 1.591 1.808 1.869 1.983 2.117 2.302 2.448

3.092 2.973 2.682 2.510 2.458 2.294 2.069 1.906 1.784 1.655 1.512 1.371 1.256 1.195 1.174 1.130 1.097 1.063 1.046 1.026 1.010 1.010 1.012 1.000

a

Standard uncertainties: u(x) = 0.001, u(y) = 0.001, u(T) = 0.05 K, u(P) = 0.1 kPa.

the measured VLE data were in good agreement with the literature2 data and the calculated data using NRTL model with the binary parameters obtained from Aspen plus V8.6 databank. Therefore, the dynamic recirculating still we used was reliable. The isobaric VLE data of the systems isobutyl alcohol (1) + DMSO (3), isobutyl acetate (2) + DMSO (3), and isobutyl alcohol (1) + isobutyl acetate (2) + DMSO (3) were measured at 101.3 kPa with the same apparatus. The VLE data and calculated activity coefficients γ1, γ2, and γ3 are listed in the Tables 4−6. 3.2. Thermodynamic Consistency Test of Experimental Data. The relationship of vapor and liquid equilibrium system can be expressed as follows29 ⎡ V L(P − P s) ⎤ ∧ i s ⎢ i ⎥ φiPyi = Pisxiγφ exp i i RT ⎣ ⎦

The value of constants C1,i−C7,i, Tmin and Tmax for the pure components obtained from Aspen plus V8.6 physical properties databank are presented in Table 7. Under atmospheric ⎡ V L(P − P s) ⎤ pressure, the Poynting factor exp⎣⎢ i RT i ⎦⎥ is approximately ∧

equal to 1, vapor phase is treated as ideal gas, so φsi and φi are assumed to be 1. Therefore, eq 1 can be simplified as

Pyi = Pisxiγi

The experimental activity coefficients listed in the Tables 4−6 are calculated by eq 3. In order to verify the reliability of the experimental data, the thermodynamic consistency test was necessary to carry out. For a binary system, Herington method30 is described by the following equation

(i = 1, 2, ...n) (1)

where yi and xi are the mole fractions of component i in the vapor and liquid phase, respectively; P is the equilibrium pressure; γi is the activity coefficient of component i in liquid

x1= 1

∧

C2, i (T /K) + C3, i

+ C6, i(T /K)C7, i

γ

∫x = 0 ln γ1 dx1 S+ − S− 1 2 D = 100 × = 100 × 1 = x γ S+ + S− ∫ 1 ln γ1 dx1

phase; φi is the vapor-phase fugacity coefficient; φsi is the pure component fugacity coefficient at saturation; ViL is the pure liquid molar volume; R is the universal gas constant; Psi is the saturation vapor pressure of component i at equilibrium temperature T, which was obtained by the extended Antoine equation ln(Pis/kPa) = C1, i +

(3)

x1= 0

J = 50 ×

ΔHm ΔGmE

×

Tmax − Tmin Tmin

2

(4)

(5)

where the values of S+ and S− refer to the area between the curve ln(γ1/γ2) − x1 and the line ln(γ1/γ2) = 0. Tmax and Tmin represent the maximum and minimum boiling temperatures of the system. ΔHm and ΔGEm denote the maximum (minimum)

+ C4, i(T /K) + C5, i(ln T /K)

(2) C



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Table 6. Experimental VLE Data of the System Isobutyl Alcohol (1) + Isobutyl Acetate (2) + DMSO (3) at Pressure P = 101.3 kPa, Temperature T, Liquid Mole Fraction x, Vapor Mole Fraction y, Activity Coefficient γa T/K

x1

x2

y1

y2

γ1

γ2

γ3

397.61 397.37 396.42 396.38 395.52 396.15 394.78 395.05 394.99 394.78 394.78 395.82 396.64 396.56 403.92 403.82 403.62 403.86 403.47 403.71 403.68 404.62 406.11 404.96 407.61 408.01 407.89 409.40

0.035 0.081 0.123 0.184 0.216 0.245 0.289 0.311 0.329 0.401 0.415 0.431 0.517 0.570 0.035 0.065 0.097 0.104 0.150 0.185 0.202 0.229 0.232 0.273 0.295 0.312 0.369 0.372

0.575 0.514 0.484 0.403 0.391 0.338 0.328 0.295 0.271 0.208 0.189 0.152 0.069 0.026 0.355 0.328 0.300 0.278 0.245 0.211 0.201 0.173 0.150 0.129 0.088 0.069 0.037 0.019

0.049 0.112 0.172 0.254 0.296 0.339 0.391 0.425 0.456 0.556 0.583 0.624 0.789 0.890 0.055 0.101 0.152 0.161 0.244 0.311 0.336 0.390 0.414 0.493 0.568 0.629 0.752 0.805

0.880 0.821 0.768 0.685 0.650 0.604 0.560 0.527 0.498 0.400 0.371 0.328 0.164 0.068 0.838 0.792 0.743 0.728 0.651 0.585 0.568 0.510 0.473 0.407 0.321 0.258 0.143 0.082

0.796 0.788 0.816 0.806 0.821 0.812 0.832 0.833 0.845 0.852 0.863 0.860 0.884 0.905 0.709 0.715 0.721 0.715 0.755 0.776 0.769 0.765 0.765 0.802 0.788 0.817 0.827 0.840

1.210 1.270 1.296 1.392 1.396 1.469 1.464 1.519 1.568 1.652 1.683 1.798 1.932 2.118 1.561 1.602 1.650 1.736 1.777 1.842 1.885 1.910 1.962 2.029 2.171 2.229 2.287 2.415

1.397 1.296 1.227 1.198 1.151 1.131 1.084 1.047 0.987 0.968 0.998 0.957 0.905 0.840 1.088 1.094 1.095 1.108 1.093 1.073 1.004 1.008 1.041 1.001 0.979 0.972 0.942 0.950

Table 8. Results of Thermodynamic Consistency Test isobutyl alcohol (1)+ DMSO (3)

parameters D J |D − J| result

12.1021 32.6277 20.5256 failed

Jcorrected |D − J|corrected result

14.8504 2.7483

(Fk)avga (Fk)maxb result

3.6916 3.9920 passed

L W F result

12.2240 13.1577 3.6786 passed

a

passed

isobutyl acetate (2) + DMSO (3)

isobutyl alcohol (1) + isobutyl acetate (2) + DMSO (3)

Herington 6.0409 28.4496 22.4087 failed Modified Herington 11.9041 5.8632 passed Wisniak Point Test 2.3863 2.9316 passed Wisniak Area Test 21.7925 22.9959 2.6869 passed

3.1427 3.5403 passed

The average value of Fk. bThe maximum value of Fk.

T10 and T20 represent the boiling points of pure components 1 and 2, respectively. Ti is the lowest boiling point in Kelvin. The ratio ΔHm/ΔGmE was calculated based on the following equations ΔHm(J ·mol−1) = − 237.02 + 1.3863 × ΔGmE(J· mol−1) (7)

a

Standard uncertainties: u(x) = 0.001, u(y) = 0.001, u(T) = 0.05 K, u(P) = 0.1 kPa.

ΔGE = RT ∑ xi ln γi

The relationship between ΔG and xi was fitted into a polynomial, as shown in Figure 2, and the value of ΔGEm was obtained by derivation. The values ΔHm/ΔGEm for binary system isobutyl alcohol (1) + DMSO (3) and isobutyl acetate (2) + DMSO (3) were 2.008 and 1.846, respectively. Using the modified Herington test, both the binary systems were found consistent. Furthermore, experimental data was evaluated by the Wisniak method,34,35 and the thermodynamic consistent point test and area test were described by the following equations

Table 7. Parameters of Extended Antoine Equationa

a

components

isobutyl alcohol

isobutyl acetate

DMSO

C1 C2 C3 C4 C5 C6 C7 Tmin/K Tmax/K

114.8720 −10504.0 0 0 −13.921 1.6898 × 10−17 6.00 165.15 547.80

65.4022 −6944.3 0 0 −7.298 3.7892 × 10−6 2.00 174.30 560.80

49.3652 −7620.6 0 0 −4.6279 4.3819 × 10−7 2.00 291.67 729.00

Fk = 100 ×

Taken from Aspen plus V8.6 physical properties databank.

excess enthalpy and extreme value of excess Gibbs energy, respectively. Herington30 concluded that the ratio ΔHm/ΔGEm rarely exceeded 3 based on measured data of 15 systems. Therefore, the value ΔHm/ΔGEm was set as 3. However, the results of Herington test in Table 8 illustrated that both binary systems were inconsistent based on the criteria31−33 |D − J| < 10. Wisniak33 reanalyzed the value of J in eq 5 based on the available data in the literatures and concluded that eq 5 should be J = 34 ×

ΔHm ΔGmE

×

T10

− Ti

(8) E

Lk =

Wk =

∑ Ti0xiΔsi0 ∑ xiΔsi0

L=

(6)

x1= 1

∫x =0 1

D

|L − W | L+W

L k dx1

(9)

−T

RT ⎛ ⎜∑ xi ln γi − ∑ xiΔsi0 ⎝

F = 100 ×

T20

|L k − Wk| L k + Wk

(10)

∑ xi ln

yi ⎞ ⎟ xi ⎠

(11)

(12)

(13) DOI: 10.1021/acs.jced.7b00241 J. Chem. Eng. Data XXXX, XXX, XXX−XXX


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Figure 2. Calculated excess free Gibbs energies of binary systems. (a) Isobutyl alcohol (1) + DMSO (3); (b) isobutyl acetate (2) + DMSO (3); □ (○), experimental data; solid line, fitted polynomial.

Table 9. Molar Entropy of Vapor sV, Molar Entropy of Liquid sL, and Molar Entropy of Vaporization Δs0 for Isobutyl Alcohol, Isobutyl Acetate, and DMSO at 101.3 kPaa

a

components

isobutyl alcohol

isobutyl acetate

DMSO

sV/J·Kmol−1·K−1 sL/J·Kmol−1·K−1 Δs0/J·Kmol−1·K−1

−400680 −510010 109330

−535530 −627850 92320

−185920 −281990 96070

Taken from Aspen Plus V8.6 physical properties databanks.

W=

x1= 1

∫x =0

Wk dx1

(14)

1

where Ti0 is the boiling point of component i at 101.3 kPa; xi and yi are liquid and vapor phase mole fractions of component i; Δs0i is the molar entropy of vaporization of component i, which is the difference of molar entropy between the vapor and liquid phase at 101.3 kPa. The values of molar entropy for each component taken from Aspen Plus V8.6 physical properties databanks are listed in Table 9. R is the universal gas constant; T is the equilibrium temperature; and k denotes experimental point. If Fk < 5, the data can be considered as thermodynamically consistent. The maximum and average values of Fk presented in Table 8 indicated that all the experimental data pass the Wisniak point test. Additionally, the binary systems passed the Wisniak area test based on the criteria F < 5.

Figure 3. Experimental and calculated T−x−y diagram of the system isobutyl alcohol (1) + DMSO (3) at 101.3 kPa: ●, experimental liquid phase; ○, experimental vapor phase; black solid line, calculated result with NRTL model; red dash line, calculated result with UNIQUAC model; blue dot line, calculated result with Wilson model.

3.3. Correlation of Binary Vapor Liquid Equilibrium. For rigorous simulation of extractive distillation, it is essential to obtain the thermodynamic model parameters from related

Table 10. Binary Interaction Parameters and Root-Mean-Square Deviations (RMSD) for Binary Systems correlation parameters model

bij

RMSD δP/kPab

bji

δT/Kb

δxb

δyb

0.224 0.235 0.229

0.002 0.002 0.002

0.002 0.001 0.001

0.362 0.389 0.369

0.008 0.007 0.007

0.006 0.006 0.005

a

NRTLc UNIQUACd Wilsone

238.150 1.350 30.142


655.581 ± 16.974 −303.660 ± 24.911 236.943 ± 14.482


146.139 ± 37.848 −257.260 ± 24.454 −332.184 ± 28.853

Isobutyl Alcohol (1) + Isobutyl Acetate (2) −82.646 −45.324 −182.843 Isobutyl Alcohol (1) + DMSO (3) −563.269 ± 6.700 0.066 266.576 ± 12.420 0.078 −103.853 ± 20.987 0.075 Isobutyl Acetate (2) + DMSO (3) 352.368 ± 43.07 0.696 61.843 ± 16.395 0.670 −203.719 ± 25.837 0.642

c cal 2 1/2 Taken from Aspen plus V8.6 databank. bδm = [(1/n)∑in= 1(mexp i − mi ) ] , n denotes the number of data points, m denotes P, T, x, y. NRTL, τij = bij/T, the value of αij was fixed at 0.3 for the binary systems. dUNIQUAC, τij = exp(bij/T). eWilson, ln Aij = bij/T a

E



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Figure 4. Experimental and calculated T−x−y diagram of the system isobutyl acetate (2) + DMSO (3) at 101.3 kPa: ●, experimental liquid phase; ○, experimental vapor phase; black solid line, calculated result with NRTL model; red dash line, calculated result with UNIQUAC model; blue dot line, calculated result with Wilson model.

Figure 5. Effect of DMSO (3) on the VLE of isobutyl alcohol (1) + isobutyl acetate (2) at 101.3 kPa: ●, experimental data (DMSO mole fraction x3 = 0); ▲, experimental data (DMSO mole fraction x3 ≈ 0.4); ▼, experimental data (DMSO mole fraction x3 ≈ 0.6); dash line, calculated result with Wilson model (DMSO mole fraction x3 = 0); dot line, calculated result with Wilson model (DMSO mole fraction x3 = 0.4); dash dot line, calculated result with Wilson model (DMSO mole fraction x3 = 0.6).

binary systems. Therefore, the binary systems isobutyl alcohol (1) + DMSO (3) and isobutyl acetate (2) + DMSO (3) were correlated with the NRTL, UNIQUAC, and Wilson models to obtain the corresponding interaction parameters by Aspen plus V8.6.36 The following objective function (F), on the basis of the maximum likelihood principle is expressed n

F=

2 ⎡ exp ⎛ P − P cal ⎞2 ⎛ T exp − T cal ⎞2 ⎛ x1,exp − x1,cali ⎞ i i i ⎟ ⎟⎟ + ⎜⎜ i ⎟⎟ + ⎜⎜ i ⎟ σP σT σx ⎠ ⎝ ⎠ ⎠ ⎝ ⎢⎣⎝

∑ ⎢⎢⎜⎜ i=1

⎛ y exp − y cal ⎞2 ⎤ 1, i 1, i ⎟ ⎥ + ⎜⎜ ⎟⎥ y σ ⎠ ⎥⎦ ⎝

(15)

where n is the number of experimental data points; P and T are the equilibrium pressure and temperature, respectively; x1 and y1 are the mole fractions of light component in the liquid and vapor phase; superscripts “exp” and “cal” denote experimental and calculated values; and σ is the standard deviation of indicated data. The standard deviations of pressure (σP), temperature (σT), liquid composition (σx1), and vapor composition (σy1) used in VLE data correlation are 0.1 kPa, 0.01K, 0.001, and 0.001. The correlated binary interaction parameters of NRTL, UNIQUAC, and Wilson models are shown in Table 10, together with the root-mean-square deviations (RMSD) of the data correlation. The comparisons between experimental and calculated data of the binary system

Figure 6. Relative volatility α21 versus isobutyl alcohol mole fraction x1′ (excluding DMSO) calculated with Wilson model at 101.3 kPa: black solid line, DMSO mole fraction x3 = 0; red solid line, DMSO mole fraction x3 = 0.2; blue solid line, DMSO mole fraction x3 = 0.36; green solid line, DMSO mole fraction x3 = 0.6.

Table 11. Mean Absolute Deviations of Equilibrium Temperature and Vapor Mole Fraction for Ternary System of Isobutyl Alcohol (1) + Isobutyl Acetate (2) + DMSO (3) maximum absolute deviations model

ΔmaxT/K

NRTL UNIQUAC Wilson

0.6441 0.8665 0.5627

c

mean absolute deviations

Δmaxy1c

Δmaxy2c

Δmaxy3c

δT/K

0.0132 0.0154 0.0130

0.0110 0.0164 0.0116

0.0092 0.0075 0.0091

0.2264 0.3561 0.1947

a

δy1b

δy2b

δy3b

0.0060 0.0063 0.0053

0.0048 0.0074 0.0057

0.0031 0.0021 0.0028

b n exp δT = (1/n)∑in= 1|Texp − Tcal − ycal i i |, where n is the number of data points, T is the equilibrium temperature. δy = (1/n)∑i = 1|yi i |, where n is the c number of data points, y is vapor-phase mole fraction. ΔmaxT and Δmaxy are the maximum deviations of temperature and vapor composition, respectively. a

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Article

are shown in Figures 3 and 4. The figures show that the calculated results agree well with those of experimental. 3.4. Prediction of Ternary System. The VLE data for the ternary system of isobutyl alcohol (1) + isobutyl acetate (2) + DMSO (3) was predicted by the correlated parameters of NRTL, UNIQUAC, and Wilson models. The experimental VLE data for the ternary system are shown in Table 6. The maximum deviations and mean absolute deviations of equilibrium temperature and vapor-phase mole fraction between experimental and calculated are given in Table 11. All three models give good prediction with reasonable deviations. It can be seen from Table 11 that the mean absolute deviations of equilibrium temperature and vapor-phase mole fraction of Wilson model are less than those of NRTL and UNIQUAC models, so Wilson model is more suitable to investigate the solvent effect in the ternary system. 3.5. Solvent Effect. DMSO was expected to be an effective entrainer to break the azetropic point formed by isobutyl alcohol and isobutyl acetate. The effect of DMSO is shown in Figures 5 and 6. In Figure 5, the vapor and liquid phase mole fractions of isobutyl alcohol y1′ and x1′ are mole fractions excluding DMSO. It is shown that isobutyl acetate becomes a more volatile component with the addition of DMSO, although the boiling point of isobutyl acetate is higher than that of isobutyl alcohol at 101.3 kPa. Figure 5 indicates that the azeotrope disappears if enough DMSO is added. Figure 6 indicates the relative volatility of isobutyl acetate to isobutyl alcohol increases with the increase of DMSO, and the minimum content of DMSO to destroy the azeotrope is 0.36. The effects of DMSO to the system of isobutyl alcohol + isobutyl acetate are caused by the different molecular interactions of isobutyl alcohol−DMSO and isobutyl acetate− DMSO. Table 6 shows that the activity coefficients of isobutyl acetate are greater than those of isobutyl alcohol in the ternary system of isobutyl alcohol + isobutyl acetate + DMSO, which indicates that the molecular interactions between isobutyl acetate and DMSO are less than those between isobutyl alcohol and DMSO, so DMSO can enhance the relative volatility of isobutyl acetate to isobutyl alcohol and make isobutyl acetate the more volatile component.

Notes

The authors declare no competing financial interest.

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4. CONCLUSION The isobaric VLE data for the binary systems isobutyl alcohol + DMSO, isobutyl acetate + DMSO and ternary system isobutyl alcohol + isobutyl acetate + DMSO were measured at 101.3 kPa. All of the binary and ternary VLE data are thermodynamically consistent. The experimental VLE data of the binary systems were correlated by NRTL, UNIQUAC, and Wilson models, and the binary interaction parameters were obtained. The ternary VLE are predicted by NRTL, UNIQUAC, and Wilson models with the corresponding correlated binary interaction parameters, and the predicted results agree well with the experimental data. The relative volatility of isobutyl acetate to isobutyl alcohol can be greatly increased by DMSO and the azeotropic point of isobutyl acetate and isobutyl alcohol can be destroyed by DMSO. The solvent DMSO is a promising entrainer for the separation of isobutyl alcohol and isobutyl acetate by extractive distillation.

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Xianbao Cui: 0000-0001-6080-2628 G



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